Dielectric composition, dielectric element, electronic component and laminated electric component

ABSTRACT

A dielectric composition, a dielectric element, an electronic component and a laminated electric component are disclosed. In an embodiment a dielectric composition has a perovskite crystal structure containing at least Bi, Na, Sr and Ti, wherein the dielectric composition includes a high-Bi phase in which the Bi concentration is at least 1.2 times the mean Bi concentration in the dielectric composition as a whole.

This patent application is a national phase filing under section 371 ofPCT/EP2016/063836, filed Jun. 16, 2016, which claims the priority ofJapanese patent application 2015-143407, filed Jul. 17, 2015, each ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a dielectric composition which includesa perovskite crystal structure and is advantageous for medium- andhigh-voltage applications with a high rated voltage, and also to adielectric element comprising the same, an electronic component and alaminated electronic component.

BACKGROUND

Recent years have seen increasing demand for miniaturization andincreased reliability of dielectric elements as electronic circuitsreach higher densities. Miniaturization of electronic components such aslaminated ceramic capacitors, together with increased capacity andhigher reliability are rapidly progressing, while the applicationsthereof are also expanding. Various characteristics are required asthese applications expand. Materials having barium titanate (BaTiO₃) asthe main component are often conventionally used as dielectriccompositions.

For example, a smoothing capacitor or a snubber capacitor such as amotor vehicle DC-DC converter or AC-DC inverter is often used in alocation in which a high DC bias of several hundred volts is applied.

There is therefore a problem with conventional electronic componentshaving a dielectric layer comprising a dielectric composition which hasBaTiO₃ as the main component in that there is a reduction in dielectricconstant when a high DC bias is applied. This problem is due to the factthat BaTiO₃ is a ferroelectric material, so the dielectric constanttends to decrease the higher the DC bias. When electronic componentshaving a dielectric layer comprising a dielectric composition which hasBaTiO₃ as the main component are used for applications involving high DCbias application it is therefore necessary to devise a method for usingsuch electronic components, for example. According to one example of aknown method, the amount of reduction in the dielectric constant isanticipated and a plurality of the electronic components is connected inparallel for use in order to maintain the required capacitance ordielectric constant.

Furthermore, in a conventional dielectric composition having BaTiO₃ asthe main component, the field intensity applied to the dielectric layeris small during use under a low DC bias such as several volts or less,so the thickness of the dielectric layers can be set to a sufficientlythin level that breakdown does not occur. This means that there areessentially no problems such as short circuiting defects which occur asa result of breakdown of the dielectric layer. However, reductions ininsulation resistance and short circuiting defects etc. caused by thedielectric composition itself become a problem during use under a highDC bias such as several hundred volts or greater. The dielectriccomposition forming the dielectric layer therefore needs to be extremelyreliable.

In the prior art, dielectric compositions having improved reliabilityhave been developed by adding a paraelectric such as barium zirconate.However, even greater reliability has become desirable in recent years.

Japanese Patent Application JP 2000-223351 A describes a laminatedceramic capacitor in which the temperature characteristics, dielectricconstant and high-temperature load lifespan are improved by setting aspecific range for the surface area ratio of a core and a shell indielectric ceramic particles having a core-shell structure.

However, the improvement in high-temperature load lifespan is inadequatewith the laminated ceramic capacitor described in Japanese PatentApplication JP 2000-223351 A and further improvements are needed.

Furthermore, Japanese Patent Application JP 2005-22891 A mentioned belowdescribes a dielectric porcelain comprising perovskite barium titanatecrystal grains in which part of the B site of BaTiO₃, which is aferroelectric material, is substituted with Zr (BTZ-type crystalgrains), and likewise comprising perovskite bismuth sodium titanatecrystal grains (BNST-type crystal grains). In that dielectric porcelain,Mg, Mn and at least one rare earth element are present in the grainboundary phase between the BTZ-type crystal grains and the BNST-typecrystal grains. In addition, the dielectric porcelain has a core-shellstructure in which the mean particle size of both the BTZ-type crystalgrains and the BNST-type crystal grains is 0.3-1.0 μm.

However, with the dielectric porcelain and laminated ceramic capacitordescribed in Japanese Patent Application JP 2005-22891 A, there is alarge reduction in dielectric constant with respect to DC bias and thedielectric constant cannot be considered adequate for use under a highvoltage, for instance in a smoothing capacitor or a snubber capacitorsuch as a motor vehicle DC-DC converter or AC-DC inverter. Furtherimprovement in the dielectric constant when a DC bias is applied istherefore needed.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a dielectric compositionwhich can be used in a power supply circuit with a high rated voltageand has an excellent dielectric constant when a DC bias is applied andan excellent high-temperature load lifespan. Further embodiments providea dielectric element comprising the same, an electronic component and alaminated electronic component.

Embodiments of the invention provide a dielectric composition having aperovskite crystal structure containing at least Bi, Na, Sr and Ti,wherein: the dielectric composition includes a high-Bi phase in whichthe Bi concentration is at least 1.2 times the mean Bi concentration inthe dielectric composition as a whole.

The dielectric composition having the abovementioned constitution has anexcellent dielectric constant when a DC bias is applied and an excellenthigh-temperature load lifespan.

Further embodiments provide α, 0<α≤0.150, where α is the surface areaproportion of the high-Bi phase in the cross section of the dielectriccomposition, with respect to the whole of said cross section.

By setting 0<α≤0.150, it is possible to further improve thehigh-temperature load lifespan.

Other embodiments provide β, 0.125≤β≤2.000, where β is the molar ratioof Bi with respect to Sr in the dielectric composition.

By virtue of the fact that 0.125≤β≤2.000 is satisfied, it is possible tofurther improve the dielectric constant when a DC bias is applied.

Various other embodiments provide a dielectric composition comprising atleast one element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho,Yb, Ba, Ca, Mg and Zn.

By virtue of the fact that the dielectric composition comprises at leastone selected from among La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba,Ca, Mg and Zn, it is possible to further improve the DC biascharacteristics.

In yet other embodiments, the content of the at least one selectedelement from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg andZn is between 1 molar part and 15 molar parts, taking the Ti content ofthe dielectric composition as 100 molar parts.

By setting the content of the at least one selected from among La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg and Zn at between 1 molarpart and 15 molar parts, it is possible to further improve the DC biascharacteristics.

In addition, the dielectric composition may comprise Li, the Li contentbeing between 0.1 molar parts and 5 molar parts, taking the Ti contentof the dielectric composition as 100 molar parts.

By setting the Li content at between 0.1 molar parts and 5 molar parts,it is possible to simultaneously improve the dielectric constant when aDC bias is applied and the high-temperature load lifespan.

A dielectric element according to embodiments of the present inventionis provided with the abovementioned dielectric composition.

An electronic component according to embodiments of the presentinvention is provided with a dielectric layer comprising theabovementioned dielectric composition.

A laminated electronic component according to embodiments of the presentinvention has a laminated portion formed by alternately laminating aninternal electrode layer and a dielectric layer comprising theabovementioned dielectric composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in cross section of a laminated ceramic capacitoraccording to an embodiment of the present invention;

FIG. 2 is an example of the cross section of a dielectric compositionaccording to an embodiment of the present invention; and

FIG. 3 is an example of the cross section of a dielectric compositionaccording to an embodiment of the present invention.

A laminated ceramic capacitor according to an embodiment of the presentinvention will be described below with reference to the figures. Itshould be noted that the dielectric composition according to embodimentsof the present invention may also be used in a dielectric element, andit may also be used in an electronic component other than a laminatedceramic capacitor, such as a single-plate capacitor.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 is a schematic cross-sectional diagram of a laminated ceramiccapacitor according to an embodiment of the present invention.

As shown in FIG. 1, a laminated ceramic capacitor 200 according to anembodiment of the present invention comprises a capacitor element mainbody 5 having a structure in which dielectric layers 7 and internalelectrode layers 6A, 6B are alternately stacked. The internal electrodelayers 6A, 6B are stacked in such a way that the end surfaces thereofare alternately exposed at the surfaces of the two opposing ends of thecapacitor element main body 5. A pair of external electrodes 11A, 11Bare formed at both ends of the capacitor element main body 5 and areconnected to the exposed end surfaces of the internal electrode layers6A, 6B which are alternately disposed, thereby forming a capacitorcircuit.

There is no particular limitation as to the shape of the capacitorelement main body 5, but it is normally a cuboid shape. Furthermore,there is no particular limitation as to the dimensions of the capacitorelement main body 5. The dimensions are normally, approximately, suchthat (long side)×(short side)×(height)=(0.6 mm-7.0 mm)×(0.3 mm-6.4mm)×(0.3 mm-2.5 mm).

The internal electrode layers 6A, 6B are stacked in such a way as to beprovided alternately with the dielectric layers 7, and in such a waythat the end surfaces thereof are alternately exposed at the surfaces ofthe two opposing ends of the capacitor element main body 5. Furthermore,the pair of external electrodes 11A, 11B are formed at both ends of thecapacitor element main body 5 and are connected to the exposed endsurfaces of the internal electrode layers 6A, 6B which are alternatelydisposed, thereby forming the laminated ceramic capacitor 200.

Furthermore, the internal electrode layers 6A, 6B comprise a conductivematerial which is a noble metal or a base metal and act essentially aselectrodes. Specifically, the conductive material which is a noble metalor a base metal is preferably any of Ag, Ag alloy, Cu or Cu alloy. Thereis no particular limitation as to metals other than Ag and Cu which areincluded in the Ag alloy or Cu alloy, but one or more metals selectedfrom Ni, Mn, Cr, Co, Al and W is preferred. Furthermore, when Ag alloyis used, the Ag content is preferably at least 95 wt %, taking said Agalloy as 100 wt %. When Cu alloy is used, the Cu content is preferablyat least 95 wt %, taking said Cu alloy as 100 wt %.

The conductive material may also contain various trace components suchas P, C, Nb, Fe, Cl, B, Li, Na, K, F, S or the like in a total amount ofno greater than 0.1 wt %.

Various conditions such as the thickness and number of internalelectrode layers 6A, 6B should be determined, as appropriate, inaccordance with the intended aim or application. The thickness of theinternal electrode layers 6A, 6B is preferably around 0.1 μm-4.0 μm andmore preferably 0.2 μm-3.0 μm.

The external electrodes 11A, 11B conduct, respectively, with theinternal electrode layers 6A, 6B which are alternately disposed insidethe capacitor element main body 5, and are formed as a pair at both endsof the capacitor element main body 5. There is no particular limitationas to the metal forming the external electrodes 11A, 11B. One type ofmetal selected from Ni, Pd, Ag, Au, Cu, Pt, Rh, Ru or Ir etc. may beused alone, or an alloy of two or more metals may equally be used. Cu,Cu alloy, Ni, Ni alloy, Ag, Ag—Pd alloy, or In—Ga alloy etc. is normallyused for the external electrodes 11A, 11B.

The thickness of the external electrodes 11A, 11B should be determined,as appropriate, in accordance with the application etc. The thickness ofthe external electrodes 11A, 11B is preferably around 10-200 μm.

The dielectric layers 7 comprise the dielectric composition according tothis embodiment. The thickness of each dielectric layer 7 may be freelyset and should be determined, as appropriate, in accordance with theintended aim or application. There is no particular limitation as to thethickness of each dielectric layer 7. The thickness may be set at 1-100μm, for example. It should be noted that the thickness of eachdielectric layer 7 is normally no greater than 30 μm and is preferablyno greater than 10 μm from the point of view of reducing the size of theelement. Furthermore, there is no particular limitation as to the numberof dielectric layers 7. This should be determined, as appropriate, inaccordance with the intended aim or application.

Here, the dielectric composition contained in the dialectic layers 7according to this embodiment has a perovskite crystal structurecontaining at least Bi, Na, Sr and Ti.

The dielectric composition having a perovskite crystal structure is apolycrystalline material comprising, as the main phase, a perovskitecompound represented by the general formula ABO₃. The A site includes atleast one selected from Bi, Na and Sr, and the B site includes at leastTi.

If the whole of the A site is taken as 100 at. %, the proportion of Bi,Na, Sr occupying the A site is preferably a total of at least 80 at. %.Furthermore, if the whole of the B site is taken as 100 at. %, theproportion of Ti occupying the B site is preferably at least 80 at. %.

As indicated above, the dielectric layers 7 according to this embodimentcomprise a dielectric composition. As shown in FIG. 2 and FIG. 3, thedielectric composition comprises sintered particles 20 not including ahigh-Bi phase 8, sintered particles 30 including a high-Bi phase 8, anda grain boundary 10. It should be noted that the dielectric compositioncontained in the dielectric layers 7 according to this embodiment is asintered dielectric composition. The sintered particles 20 not includinga high-Bi phase and the sintered particles 30 including a high-Bi phaseare also referred to collectively below as the “sintered particles 20,30”.

Here, the dialectic composition comprises a high-Bi phase 8 in which theBi concentration is at least 1.2 times the mean Bi concentration of thedielectric composition as a whole.

Furthermore, in addition to the sintered particles 20, 30 and the grainboundary 10, the dielectric composition may also include pores (airholes) (not depicted). Oxygen is substantially absent from the pores.There is no particular limitation as to the cross-sectional area of thepores, but a value of 5% or less as a surface area proportion withrespect to the dielectric composition as a whole is preferred.

The high-Bi phase 8 may be included in the dielectric composition in anyform. For example, as shown in FIG. 2, the high-Bi phase 8 may beincluded in the sintered particles. As shown in FIG. 3, the high-Biphase 8 may be included in the grain boundary 10. The high-Bi phase 8may of course be included in both the sintered particles and the grainboundary 10.

There is no particular upper limit to the Bi concentration in thehigh-Bi phase 8, but a value of no greater than 2.0 times the mean Biconcentration is preferred.

The dielectric composition according to this embodiment has a high-Biphase 8, and as a result the dielectric constant when a DC bias isapplied is maintained in a preferred range while the high-temperatureload lifespan is also improved.

On the other hand, a dielectric composition in which the high-Bi phase 8is absent has a reduced high-temperature load lifespan and reducedreliability in comparison with a dielectric composition in which thehigh-Bi phase 8 is present.

An example of a method for distinguishing the high-Bi phase 8, a methodfor determining whether or not a high-Bi phase 8 is present, and amethod for calculating the surface area proportion a occupied by thehigh-Bi phase 8 will be described below.

Using scanning transmission electron microscopy (STEM), an observationfield is first of all set in the cross section of the dielectric layers7 cut at the location of intersection with the internal electrode layers6A, 6B.

There is no particular limitation as to the surface area of theobservation field, but a surface area including around 20-50 of thesintered particles 20, 30 is preferred from the point of view of EDSanalysis accuracy and analysis efficiency. To be specific, theobservation field preferably has a size of the order of 5 m×5 μm.Furthermore, the magnification of the observation field is preferablybetween 10,000 and 50,000 times.

Composition mapping analysis is then carried out in the wholeobservation field by means of energy dispersive X-ray spectroscopy(EDS), and the X-ray spectrum for elemental Bi is measured. The meanconcentration of elemental Bi included in the observation field as awhole (mean Bi concentration) is calculated from the resulting X-rayspectrum. A mapping image for the elemental Bi is then subjected toimage processing in such a way that it is possible to distinguishregions in which the elemental Bi concentration is at least 1.2 timesthe mean Bi concentration (high-Bi phase 8) and regions in which thevalue is less than 1.2 times.

The surface area proportion a occupied by the high-Bi phase 8 withrespect to the field as a whole is then calculated from the mappingimage which has undergone image processing. Specifically, the surfacearea proportion a with respect to the field as a whole is calculated byselecting all of the high-Bi phases in the mapping image and countingthe number of pixels occupied by the selected regions.

In this application, if a high-Bi phase 8 is present somewhere in theobservation field as a whole, a high-Bi phase in which the Biconcentration is at least 1.2 times the mean Bi concentration of thedielectric composition as a whole is deemed to be included. Conversely,if a high-Bi phase 8 is not present anywhere in the observation field asa whole, a high-Bi phase in which the Bi concentration is at least 1.2times the mean Bi concentration of the dielectric composition as a wholeis deemed not to be included.

It should be noted that a high-Bi phase 8 which is not apparent in themapping image is deemed to be absent because the cross-sectional area isnot large enough to satisfy the cross-sectional area corresponding toone pixel.

An example of a method for distinguishing the high-Bi phase 8 and amethod for calculating the surface area proportion a occupied by thehigh-Bi phase 8 has been described above, but there is no particularlimitation as to the method for distinguishing the high-Bi phase 8 andthe method for calculating the surface area proportion a occupied by thehigh-Bi phase 8. Transmission electron microscopy (TEM) may equally beused instead of STEM, for example.

It should be noted that it is possible to appropriately control theformation or otherwise of the high-Bi phase 8 and the surface areaproportion a by means of the make-up of the dielectric composition andthe method for producing same, and also the baking conditions etc. Forexample, by including a starting material powder having a large particlesize or performing baking at a relatively low temperature, it ispossible to promote formation of the high-Bi phase 8. Furthermore, byadding Li as a second auxiliary component to be described later, it ispossible to promote formation of the high-Bi phase 8 especially at thegrain boundary 10.

The surface area proportion a is preferably such that 0<α≤0.150. When0<α≤0.150 is satisfied, it is possible to further improve thehigh-temperature load lifespan. The surface area proportion a is morepreferably such that 0.001≤α≤0.150.

Furthermore, the dielectric composition according to this embodiment ispreferably such that the molar ratio β of the Bi content with respect tothe Sr content satisfies 0.125≤β≤2.00. When β is within theabovementioned range, the dielectric constant when a DC bias is appliedis further improved.

Furthermore, the dielectric composition according to this embodiment mayinclude at least one selected from among La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Yb, Ba, Ca, Mg and Zn (also referred to below as the “firstauxiliary component”). By incorporating the first auxiliary component,the DC bias characteristics are further improved.

The content of the first auxiliary component is preferably between 1molar part and 15 molar parts, taking the Ti content of the dielectriccomposition as 100 molar parts. When the content of the first auxiliarycomponent is within the abovementioned range, the DC biascharacteristics are further improved. The content of the first auxiliarycomponent is more preferably between 1 molar part and 10 molar parts.

Furthermore, the dielectric composition according to this embodiment mayalso include Li (also referred to below as the “second auxiliarycomponent”). The content of the second auxiliary component is preferablybetween 0.1 molar parts and 5 molar parts, taking the Ti content of thedielectric composition as 100 molar parts. When the content of thesecond auxiliary component is within the abovementioned range, thehigh-temperature load lifespan is further improved. The content of thesecond auxiliary component is more preferably between 1 molar part and 5molar parts.

There is no particular limitation as to the method for producing thelaminated ceramic capacitor according to this embodiment. For example,it is produced in the same way as a conventional laminated ceramiccapacitor, namely by preparing a green chip using a normal sheet methodor printing method employing a paste, baking the green chip and thenprinting or transcribing external electrodes and then baking. The methodfor producing the laminated ceramic capacitor will be described inspecific terms below.

There is no particular limitation as to the type of paste for thedielectric layers. For example, said paste may be an organic paintcomprising a mixture of a dielectric starting material and an organicvehicle, or it may be an aqueous paint comprising a mixture of adielectric starting material and an aqueous vehicle.

For the dielectric starting material, it is possible to use a metalcontained in the abovementioned dielectric composition, for example, anoxide of a metal selected from the group consisting of Bi, Na, Sr, Ti,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg, Zn, and Li, or amixture thereof, or a composite oxide may be used. In addition, thedielectric starting material may be appropriately selected from varioustypes of compounds which form the abovementioned oxides or compositeoxides as a result of baking, e.g., carbonates, oxalates, nitrates,hydroxides and organometallic compounds etc. and these may be mixed foruse. A powder having a mean particle size of the order of 0.1-3 μm isused as the dielectric starting material. The dielectric startingmaterial is preferably a powder having a mean particle size of 0.1-1 μm.Furthermore, the mean particle size of the dielectric starting materialmay be adjusted by appropriately varying the time for which saidmaterial is mixed.

When the paste for the dielectric layers is an organic paint, thedielectric starting material and an organic vehicle in which a binder orthe like is dissolved in an organic solvent should be mixed. There is noparticular limitation as to the binder which is used in the organicvehicle, and it may be appropriately selected from various conventionalbinders such as ethyl cellulose and polyvinyl butyral. Furthermore,there is no particular limitation as to the organic solvent which isused in the organic vehicle, and it may be appropriately selected fromvarious types of organic solvents such as terpineol, butyl carbitol,acetone and toluene, in accordance with the method which is used, namelythe printing method or sheet method etc.

Furthermore, when the paste for the dielectric layers is an aqueouspaint, the dielectric starting material and an aqueous vehicle in whicha water-soluble binder and a dispersant etc. are dissolved in watershould be mixed. There is no particular limitation as to thewater-soluble binder which is used in the aqueous vehicle, and it ispossible to use polyvinyl alcohol, cellulose or water-soluble acrylicresin, for example.

The paste for the internal electrode layers is prepared by mixing aconductive material comprising various metals or alloys described above,or various types of oxide which form the conductive material afterbaking, organometallic compounds, resinates, and the like, with theabovementioned organic vehicle or aqueous vehicle. The paste for theexternal electrodes may be prepared in the same way as the paste for theinternal electrode layers.

When an organic vehicle is used to prepare the abovementioned pastes,there is no particular limitation as to the content of said organicvehicle. For example, the binder may be present in an amount of theorder of 1-5 wt % and the organic solvent may be present in an amount ofthe order of 10-50 wt %, with respect to the dielectric startingmaterial. Furthermore, the pastes may contain additives selected fromvarious types of dispersants, plasticizers, dielectrics, and insulatorsetc., as required. The total content of these additives is preferably nogreater than 10 wt %.

When a printing method is used, the paste for the dielectric layers andthe paste for the internal electrode layers are printed alternately andrepeatedly on a substrate made of polyethylene terephthalate (PET) orthe like. After the printing, the pastes are cut to a predeterminedshape, after which they are peeled from the substrate to form a greenchip.

When the sheet method is used, a green sheet is formed using the pastefor the dielectric layers, and the paste for the internal electrodelayers is printed on the green sheet. After this, the green sheets arepeeled, stacked and cut to form a green chip.

Before the green chip is baked, a debinding treatment is performed.There is no particular limitation as to the conditions of the debindingtreatment and it should be carried out under normal conditions.

The debinding treatment is preferably carried out under a reducingatmosphere when a base metal alone or an alloy comprising a base metal,such as Cu or Cu alloy, is used for the conductive material of theinternal electrode layers. There is no particular limitation as to thetype of reducing atmosphere, and it is possible to use humidified N₂ gasor a mixed gas comprising humidified N₂ and H₂, among others.

There is no particular limitation as to the temperature increase rate,holding temperature and temperature holding time in the debindingtreatment. The temperature increase rate is preferably 0.1-100° C./hrand more preferably 1-10° C./hr. The holding temperature is preferably200-500° C. and more preferably 300-450° C. The temperature holding timeis preferably 1-48 hours and more preferably 2-24 hours. The organiccomponent such as the binder component is preferably removed down toaround 300 ppm by means of the debinding treatment, and more preferablyremoved down to around 200 ppm.

The baking atmosphere when the green chip is baked to obtain thecapacitor element main body should be appropriately determined inaccordance with the type of conductive material in the paste for theinternal electrode layers.

When a base metal alone or an alloy comprising a base metal, such as Cuor Cu alloy, is used as the conductive material in the paste for theinternal electrode layers, the oxygen partial pressure in the bakingatmosphere is preferably set at 10⁻⁶ to 10⁻⁸ atm. By setting the oxygenpartial pressure at 10⁻⁸ atm or greater, it is possible to restrictdegradation of the perovskite crystal structure contained in thedielectric composition and a reduction in the high-temperature loadlifespan. Furthermore, by setting the oxygen partial pressure at 10⁻⁶atm or less, it is possible to restrict oxidation of the internalelectrode layers.

Furthermore, the holding temperature during baking is 900-1400° C.,preferably 900-1200° C., and more preferably 1000-1100° C. By settingthe holding temperature at 900° C. or greater, this makes densificationmore likely to progress adequately due to baking. Furthermore, when theholding temperature is set at 1200° C. or less, this facilitatessuppressing diffusion of the various materials forming the internalelectrode layers and abnormal sintering of the internal electrodelayers. By suppressing abnormal sintering of the internal electrodelayers, this facilitates preventing breakage of the internal electrodes.By suppressing diffusion of the various materials forming the internalelectrode layers, this facilitates preventing a reduction in thehigh-temperature load lifespan.

By appropriately setting the holding temperature during baking in theabovementioned temperature range, this makes it easier to control thecrystal grain size, as appropriate. Furthermore, there is no particularlimitation as to the baking atmosphere. The baking atmosphere ispreferably a reducing atmosphere so as to restrict oxidation of theinternal electrode layers. There is no particular limitation as to theatmospheric gas. A mixed gas comprising N₂ and H₂ which is humidified ispreferably used as the atmospheric gas, for example. Furthermore, thereis no particular limitation as to the baking time.

Annealing (reoxidation) may be carried out after the baking during theproduction of the laminated ceramic capacitor according to thisembodiment. The annealing should be carried out under normal conditions.There is no particular limitation as to the annealing atmosphere, but anatmosphere in which the dielectric layers are oxidized and the internalelectrode layers are not oxidized is preferred. Humidified N₂ gas or amixed gas comprising humidified N₂ and H₂ etc. may be used, for example.

A wetter or the like should be used in order to humidify the N₂ gas orthe mixed gas comprising N₂ and H₂ etc. in the abovementioned debindingtreatment, baking and annealing. In this case, the water temperature ispreferably around 20-90° C.

The debinding treatment, baking and annealing processes may be carriedout successively or independently. When these processes are performedsuccessively, the following procedure is preferred, namely that thedebinding treatment is performed, after which the atmosphere is modifiedwithout cooling and then baking is carried out by raising thetemperature to the holding temperature for baking. On the other hand,when these processes are performed independently, the followingprocedure is preferred, namely that during baking the temperature israised under an N₂ gas atmosphere to the holding temperature for thedebinding treatment, after which the atmosphere is modified to theatmosphere for baking, and after the atmosphere has been modified,temperature increase is continued to the holding temperature for baking.After the baking, cooling is performed to the holding temperature forthe debinding treatment, after which the atmosphere is once againmodified to an N₂ gas atmosphere and cooling is further continued. Itshould be noted that the abovementioned N₂ gas may or may not behumidified.

The end surfaces of the capacitor element main body obtained in this wayare polished by means of barrel polishing or sandblasting, for example,the paste for the external electrodes is printed or transcribed thereon,baking is carried out and the external electrodes are formed. The pastefor the external electrodes is preferably baked at 600-800° C. foraround 10 minutes to 1 hour under a humidified mixed gas comprising N₂and H₂, for example. A coating layer is then formed on the externalelectrode surface, as required. The coating layer is formed by means ofplating or the like.

A laminated ceramic capacitor according to an embodiment of the presentinvention and a method for producing same have been described above, butthe present invention is in no way limited to this embodiment andvarious embodiments may of course be implemented within a scope thatdoes not depart from the present invention.

The dielectric element, electronic component and laminated electroniccomponent according to embodiments of the present invention areadvantageously used in a location where a relatively high rated voltageis applied. For example, they may be advantageously used in a powersupply circuit having a high rated voltage, such as in a DC-DC converteror an AC-DC inverter, for example.

Furthermore, there is no particular limitation as to the application ofthe laminated ceramic capacitor according to an embodiment of thepresent invention. For example, it may be used in a snubber capacitorfor circuit protection for which there is a need for a high dielectricconstant when a high DC bias is applied, or it may be used in asmoothing capacitor for an AC-DC inverter that converts alternatingcurrent to direct current.

Furthermore, the laminated ceramic capacitor according to thisembodiment is mounted on a printed circuit board or the like by means ofsoldering etc. The printed circuit board is then used in variouselectronic devices, e.g., a digital television or a modem etc.

In addition, the dielectric composition according to embodiments of thepresent invention does not contain lead. The inventive dielectriccomposition, dielectric element, electronic component and laminatedelectronic component are therefore also superior from an environmentalpoint of view.

The present invention will be described below in further detail with theaid of exemplary embodiments and comparative examples. However, thepresent invention is not limited by the following exemplary embodiments.It should be noted that, according to embodiments of the presentinvention, the DC field applied to the dielectric composition,dielectric element, electronic component and laminated electroniccomponent is referred to as a DC (direct current) bias. Furthermore, therate of change in the dielectric constant before and after applicationof the DC bias is referred to as the DC bias characteristics. The DCbias characteristics are better the smaller the absolute value of therate of change of the dielectric constant.

The following starting material powders were prepared as startingmaterials for producing dielectric layers: bismuth oxide (Bi₂O₃), sodiumcarbonate (Na₂CO₃), strontium carbonate (SrCO₃), barium carbonate(BaCO₃), calcium carbonate (CaCO₃), magnesium carbonate (MgCO₃), zincoxide (ZnO), lanthanum hydroxide (La(OH)₃), neodymium oxide (Nd₂O₃),samarium oxide (Sm₂O₃), gadolinium oxide (Gd₂O₃) and titanium oxide(TiO₂).

The abovementioned starting material powders were weighed out in such away that the baked dielectric compositions had the make-up shown intable 1.

The weighed starting material powders were then wet-mixed using a ballmill, after which the resulting mixtures were calcined for 2 hours underthe air at 750° C.-850° C. to obtain calcined powders.

Li₂CO₃ was then prepared as a Li starting material powder constituting asecond auxiliary component. The starting material powder was weighed outin such a way that the compositions after baking conformed to thecompositions shown in table 1, and said starting material powder wasmixed with the abovementioned calcined powders to obtain mixed powders.

An organic solvent and an organic vehicle were then added to the mixedpowders, the material was wet-mixed using a ball mill and paste fordielectric layers was prepared. At the same time, Ag powder, Ag—Pd alloypowder or Cu powder was mixed with an organic vehicle as a conductivematerial powder, and pastes for internal electrode layers comprising Ag,Ag—Pd alloy or Cu were prepared. The paste for dielectric layers wasthen moulded into sheets by means of a sheet-moulding method, andceramic green sheets were obtained.

The paste for the internal electrode layers was coated on the ceramicgreen sheets by means of screen printing to print the internal electrodelayers. The ceramic green sheets on which the internal electrode layershad been printed were then stacked, after which they were cut to apredetermined shape, whereby laminated green chips were prepared. Thelaminated green chips were subjected to debinding at 300° C.-500° C. toremove the organic component down to around 300 ppm. After thedebinding, baking was carried out under the atmosphere or under areducing atmosphere at a baking temperature of 900° C.-1400° C. Thebaking time was varied as appropriate. A mixed gas comprising humidifiedN₂ and H₂ was used as the atmospheric gas when baking was carried outunder a reducing atmosphere.

The end surfaces of the resulting laminated ceramic baked articles werepolished, after which In—Ga was applied thereto as the externalelectrodes, and samples of the laminated ceramic capacitor shown in FIG.1 were obtained. The size of the resulting laminated ceramic capacitorsamples was 3.2 mm×1.6 mm×0.6 mm, the thickness of the dielectric layerswas 20 μm, the thickness of the internal electrode layers was 1.5 μm,and there were four dielectric layers interposed between the internalelectrode layers.

It should be noted that when the dielectric layers of the laminatedceramic baked articles were dissolved by means of a solvent and analysedby means of ICP optical emission spectroscopy, it was confirmed that thecomposition of the dielectric layers was the same as the compositionsshown in table 1.

Furthermore, a cross section at the intersection of the internalelectrode layers was cut from the laminated ceramic baked articles andthe crystal structure of the dielectric layers at that cross section wasmeasured and analysed by means of X-ray diffraction. As a result, it wasconfirmed that the dielectric layers of the laminated ceramic bakedarticles comprised a composition having a perovskite crystal structure.

The surface area proportion of the high-Bi phase and the meanconcentration of elemental Bi were then measured using the methoddescribed below for each of the laminated ceramic baked articlesobtained. The dielectric constant, DC bias characteristics andhigh-temperature load lifespan were then measured using the methoddescribed below.

A cross section at the intersection of the internal electrode layers wasfirst of all cut from the laminated ceramic baked articles obtained, andthe cross sections which had been cut were cut into flakes by means of agallium ion beam to prepare samples for cross-sectional observation.

Surface Area Proportion a of the High-Bi Phase

The cross section of the dielectric layers cut at the position ofintersection with the internal electrode layers was observed by means ofscanning transmission electron microscopy (STEM). It should be notedthat the observation field was 5 m×5 μm and the magnification was 30 000times. Mapping analysis was performed in the whole field set in thecross section of the dielectric layers by means of energy dispersiveX-ray spectroscopy (EDS), and the X-ray spectrum of elemental Bi wasmeasured. The mean concentration of elemental Bi included in the wholefield was calculated from the resulting X-ray spectrum. A mapping imagefor the elemental Bi was then subjected to image processing in such away as to distinguish a phase in which the elemental Bi concentrationwas at least 1.2 times the mean concentration (high-Bi phase) and aphase in which the value was less than 1.2 times. The surface areaproportion a occupied by the high-Bi phase in the field as a whole wasthen calculated from the image which had undergone image processing. Thesurface area proportion a with respect to the field as a whole wascalculated by counting the number of pixels occupied by the high-Biphase in the image which had undergone image processing, and dividingthis number by the total number of pixels in the field as a whole. Theresults are shown in table 1.

Dielectric Constant ε1

The capacitance of the laminated ceramic capacitor samples was measuredat 25° C. and a frequency of 1 kHz by inputting a signal having an inputsignal level (measurement voltage) of 1 Vrms using a digital LCR meter(Hewlett-Packard; 4284A). The dielectric constant ε1 (no units) was thencalculated from the measured capacitance, surface area of facingelectrodes and interlayer distance. In the present exemplaryembodiments, the mean value calculated from 10 laminated ceramiccapacitor samples was used as the dielectric constant ε1. The resultsare shown in table 1.

Dielectric Constant ε2

The dielectric constant ε2 (no units) was calculated from thecapacitance measured from conditions of frequency 1 kHz and input signallevel (measurement voltage) 1.0 Vrms, surface area of facing electrodesand interlayer distance, while a DC bias generator (GLASSMAN HIGHVOLTAGE; WX10P90) was connected to a digital LCR meter (Hewlett-Packard;4284A) and a DC bias of 8 V/μm was applied to the laminated ceramiccapacitor samples. In the present exemplary embodiments, the mean valuecalculated from 10 laminated ceramic capacitor samples was used as thedielectric constant ε2. A value of 800 or greater for the dielectricconstant ε2 was deemed to be good and a value of 1000 or greater wasdeemed to be better in the present exemplary embodiments. The resultsare shown in table 1.

DC Bias Characteristics

The DC bias characteristics were calculated by means of the followingformula (1) using the dielectric constant ε1 and the dielectric constantε2. Although superior DC bias characteristics are not essential forachieving the aim of embodiments of the present invention, a smallerabsolute value for the DC bias characteristics is preferable. DC biascharacteristics within ±30% were deemed to be good in the presentexemplary embodiments. It should be noted that it is not realistic forthe DC bias characteristics to exceed +30%. There is thereforeessentially no upper limit to the preferred range for the DC biascharacteristics.DC bias characteristics (%)=100×(ε2−ε1)/ε1  Formula (1)

High-Temperature Load Lifespan

The high-temperature load lifespan was measured for the laminatedceramic capacitor samples by maintaining a state of DC voltageapplication under an electric field of 50 V/μm at 150° C. In the presentexemplary embodiments, the high-temperature load lifespan was defined asthe time from the start of DC voltage application until the insulationresistance fell to a single digit. Furthermore, the high-temperatureload lifespan was measured for 10 laminated ceramic capacitor samplesand the mean value thereof was calculated. A value of 20 hours orgreater was deemed to be good, a value of 30 hours or greater was deemedto be better, and a value of 35 hours or greater was deemed to be evenbetter in the present exemplary embodiments. The results are shown intable 1.

TABLE 1 First auxiliary Second High- Surface area component auxiliary DCbias temperature High-Bi phase proportion Molar ratio β Amount componentDielectric Dielectric charac- load ◯: present α of high- of Bi with(molar Li (molar constant constant teristics lifespan Sample no. X:absent Bi phase respect to Sr Type parts) parts) ε1 ε2 (%) (hr)Exemplary ◯ 0.179 2.833 — — — 1916 802 −58.1 23 Embodiment 1 Exemplary ◯0.161 2.000 — — — 1848 1042 −43.8 22 Embodiment 2 Exemplary ◯ 0.0010.125 — — — 1547 1053 −31.9 31 Embodiment 3 Exemplary ◯ 0.150 1.500 — —— 2100 1400 −33.3 30 Embodiment 4 Exemplary ◯ 0.052 1.167 — — — 24851318 −47.0 32 Embodiment 5 Exemplary ◯ 0.054 1.167 La 1 — 2035 1455−28.5 33 Embodiment 6 Exemplary ◯ 0.076 1.167 La 15 — 1907 1795 −5.9 34Embodiment 7 Exemplary ◯ 0.031 0.500 La 15 — 1233 1009 −18.2 30Embodiment 8 Exemplary ◯ 0.040 0.500 La 15 0.1 1200 1005 −16.3 37Embodiment 9 Exemplary ◯ 0.085 0.500 La 15 5.0 1160 1002 −13.6 42Embodiment 10 Exemplary ◯ 0.065 2.000 Sm 5 — 1729 1552 −10.2 32Embodiment 11 Exemplary ◯ 0.063 2.000 Nd 5 — 1717 1541 −10.3 33Embodiment 12 Exemplary ◯ 0.072 2.000 Gd 5 — 1735 1511 −12.9 31Embodiment 13 Exemplary ◯ 0.033 0.711 Mg 5 — 2374 1827 −23.0 34Embodiment 14 Exemplary ◯ 0.030 0.711 Zn 5 — 2118 1748 −17.5 34Embodiment 15 Exemplary ◯ 0.044 0.625 Ba 10 — 1912 1745 −8.7 31Embodiment 16 Exemplary ◯ 0.042 0.625 Ca 10 — 1880 1608 −14.5 33Embodiment 17 Comparative X — 2.000 La 5 — 1783 1794 0.6 16 Example 1Comparative X — 2.833 — — — 1944 856 −56.0 15 Example 2

It can be seen from table 1 that the laminated ceramic capacitorsaccording to Exemplary Embodiments 1-17 in which a high-Bi phase waspresent exhibited a dielectric constant ε2 when a DC bias of 8 V/μm wasapplied of 800 or greater and a high-temperature load lifespan of 20hours or greater.

Furthermore, the laminated ceramic capacitors according to ExemplaryEmbodiments 3-17 in which the surface area proportion a of the high-Biphase was such that 0<α≤0.150 exhibited a high-temperature load lifespanof 30 hours or greater, and this was an even better high-temperatureload lifespan.

On the other hand, the laminated ceramic capacitors according toComparative Examples 1 and 2 in which a high-Bi phase was not presentexhibited a high-temperature load lifespan of less than 20 hours.

Furthermore, the laminated ceramic capacitors according to ExemplaryEmbodiments 2-17 in which the molar ratio β of Bi with respect to Sr wassuch that 0.125≤β≤2.000 exhibited a dielectric constant ε2 when a DCbias of 8 V/μm was applied of 1000 or greater, and this was even better.

The laminated ceramic capacitors according to Exemplary Embodiments 6-17comprising between 1 molar part and 15 molar parts of the firstauxiliary component exhibited DC bias characteristics within ±30%. Thatis to say, the laminated ceramic capacitor samples comprising the firstauxiliary component exhibited a good dielectric constant ε2 when a DCbias was applied, a good high-temperature load lifespan, and also goodDC bias characteristics.

Furthermore, the laminated ceramic capacitors according to ExemplaryEmbodiments 9 and 10 comprising between 0.1 molar parts and 5 molarparts of the second auxiliary component exhibited a high-temperatureload lifespan of 35 hours or greater, and this was even better.

The invention claimed is:
 1. A dielectric composition comprising: aperovskite crystal structure containing at least Bi, Na, Sr and Ti,wherein the dielectric composition includes a high-Bi phase in which aBi concentration is at least 1.2 times a mean Bi concentration in thedielectric composition as a whole.
 2. The dielectric compositionaccording to claim 1, wherein 0<α≤0.150, where α is a surface areaproportion of the high-Bi phase in a cross section of the dielectriccomposition, with respect to the whole of the cross section.
 3. Thedielectric composition according to claim 1, wherein 0.125≤β≤2.000,where β is a molar ratio of Bi with respect to Sr in the dielectriccomposition.
 4. The dielectric composition according to claim 1, furthercomprising at least one element selected from the group consisting ofLa, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg and Zn.
 5. Thedielectric composition according to claim 4, wherein a content of theelement is between 1 molar part and 24 molar parts, taking a Ti contentof the dielectric composition as 100 molar parts.
 6. The dielectriccomposition according to claim 1, further comprising Li, wherein a Licontent is between 0.1 molar parts and 14 molar parts, taking a Ticontent of the dielectric composition as 100 molar parts.
 7. Adielectric element comprising the dielectric composition according toclaim
 1. 8. An electronic component comprising a dielectric layercomprising the dielectric composition according to claim
 7. 9. Alaminated electronic component comprising: a laminated portion formed byalternately laminating an internal electrode layer and a dielectriclayer comprising the dielectric composition according claim
 1. 10. Asingle-plate capacitor comprising the dielectric composition accordingto claim
 1. 11. A laminated ceramic capacitor comprising: a capacitorelement main body having a structure in which dielectric layerscomprising the dielectric composition according to claim 1 and internalelectrode layers are alternately stacked; and a pair of terminalelectrodes located at both ends of the capacitor element main body andconnected to exposed end surfaces of the internal electrode layers whichare alternately disposed, thereby forming a capacitor circuit.
 12. Thelaminated ceramic capacitor according to claim 11, wherein a conductivematerial of the internal electrode layers comprises Cu.
 13. Thelaminated ceramic capacitor according to claim 11, wherein a conductivematerial of the internal electrode layers comprises a Cu alloy.
 14. Thelaminated ceramic capacitor according to claim 11, wherein a base metalis used as a conductive material for the internal electrode layers. 15.The laminated ceramic capacitor according to claim 11, wherein theterminal electrodes comprise Cu.
 16. The laminated ceramic capacitoraccording to claim 11, wherein the terminal electrodes comprise a Cualloy.
 17. A method for producing a laminated ceramic capacitor, themethod comprising: preparing a green chip using a sheet method or aprinting method employing a paste for dielectric layers and a paste forinternal electrodes, wherein the paste for the dielectric layers is anorganic paint comprising a mixture of a dielectric starting material andan organic vehicle or wherein the paste for the dielectric layers is anaqueous paint comprising a mixture of a dielectric starting material andan aqueous vehicle; performing a debinding treatment on the green chip;baking the green chip thereby forming a main body; printing ortranscribing external electrodes on the main body; and baking the mainbody, wherein the dielectric starting material is selected such that abaked dielectric composition has a perovskite crystal structurecontaining at least Bi, Na, Sr and Ti, and wherein the dielectriccomposition includes a high-Bi phase in which a Bi concentration is atleast 1.2 times a mean Bi concentration in the dielectric composition asa whole.
 18. The method according to claim 17, wherein a base metalalone or an alloy comprising a base metal is used for a conductivematerial of the internal electrodes.
 19. The method according to claim17, wherein Cu is used for a conductive material of the internalelectrodes.
 20. The method according to claim 17, wherein a Cu alloy isused for a conductive material of the internal electrodes.